1. Field of the Invention
This invention relates to antennas, and more specifically to antennas for use within handheld or portable wireless communication devices or handsets.
2. Description of the Related Art
State of the art cellular communication systems generally require handsets that provide both a multi-band and a multi-system capability. That is, there is a growing need for multi-purpose cellular handsets that can be utilized in cellular applications such as Advanced-Mobile-Phone-Service (AMPS), Personal-Communications-Service (PCS), Global-System-For-Mobile-Communication (GSM), Distributed-Communications-System (DCS) and Industrial Scientific Medical (ISM), and that can also be utilized in non cellular applications such as Global-Positioning-System (GPS) and Bluetooth (BT) (Bluetooth is the code name for an open specification to standardize data synchronization between disparate personal computer and handheld personal computer devices).
Current advances in cellular communication technology also provide an emphasis on providing an antenna that is internal to a cellular handset, to thereby utilize the inherent advantages that are provided by such an antenna that is buried with the wireless communication device.
The structure and arrangement that is provided by the present invention includes a planar inverted-F antenna (PIFA).
A PIFA is a compact, low profile, microstrip antenna, and it is called an inverted-F antenna because a side view of the antenna resembles the letter F facing down. U.S. Pat. Nos. 6,072,434, 6,218,991 and 6,222,496, incorporated herein by reference, are examples of PIFAs.
Multi-Band PIFAs are of interest to the mobile wireless communication industry. In a multi-band PIFA a choice between providing a single antenna feed, or providing multiple antenna feeds, tends to be dependent on system requirements. However, from the standpoint of antenna design, the choice between providing a single antenna feed or multiple antenna feeds has both merits and demerits.
In a single antenna feed, multi-band, PIFA providing a required bandwidth at multiple resonant frequencies generally leads to antenna design complexities.
On the other hand, a multi-band PIFA having multiple antenna feeds tends to diminish antenna design complexities since the design of a plurality of individual radiating/receiving elements, each having a separate feed, tends to be less difficult. However, multiple antenna feeds encounter the problem of mutual coupling between the individual radiating/receiving elements of a multi-band. PIFA. There is also a concern that a multi-band PIFA with multiple antenna feed ports may have its performance compromised due to mutual coupling and poor isolation between the PIFA""s various resonant bands.
Hence, in spite of the reduced design complexities that are provided by a multi-band PIFA having multiple feeds, such a PIFA has not been a choice for practical applications, mainly due to the mutual coupling problem. In view of this, techniques that reduce the mutual coupling between the individual radiating/receiving elements of such as multi-band PIFA are important.
Past research on dual-feed, dual-band, PIFAs has emphasized optimizing the PIFA for cellular applications. However, most of the prior art dual-feed, dual-band, PIFAs exhibit an isolation of only about 15 dB.
Further improvement in the isolation that is provided by a dual-feed. dual-band, PIFA has been realized by increasing the physical separation between the antenna""s multiple radiating/receiving elements. However, such an option contradicts the desirable requirement that the overall physical volume that is occupied by the PIFA be small.
Therefore, techniques which accomplish the desired objective of improved isolation without increasing the overall volume and/or linear dimensions of a multi-band PIFA are needed by the art.
The design and application of a dual-feed, dual-band, PIFA for cellular or mobile communication have been dealt with in the following publications, wherein the publications generally deal with the design of PIFA for cellular bands such as the AMPS/PCS or GSM/DCS bands.
[1] Z. D. Liu, P. S. Hall and D. Wake, xe2x80x9cDual-Frequency Planar Inverted-F Antennaxe2x80x9d, IEEE Trans. Antennas and Propagation Vol. AP-45, No. 10, pp. 1451-1458, October 1997.
[2] C. B. Rowelland R. D. Murch,xe2x80x9cA Compact PIFA Suitable for Dual-frequency 900/1800xe2x80x94MHz Operationxe2x80x9d, IEEE Trans. Antennas and Propagation Vol. AP-46, No. 10, pp.596-598, April 1998.
[3] P. Kabacik and A. A. Kucharski,xe2x80x9cOptimizing the radiation Pattern Of Dual Frequency Inverted F Planar antennasxe2x80x9d, JINA conference, pp.655-658, 1998.
[4] P. Song, P. S. Hall, H. Ghafouri-Shiraz and D. Wake, xe2x80x9cTriple-Band Planar Inverted F Antennaxe2x80x9d, IEEE-APS Symposium, 1999, Orlando, pp.908-911.
Above cited reference [1] discusses an achievable isolation between the two feed ports of a GSM/DCS band PIFA. Specifically, isolation between the two ports as reported in [1] is of the order of about 15 dB. Any improvement in the isolation, while maintaining the overall volume of the PIFA, is at the expense of gain at one of the antenna ports.
To the contrary, the present invention improves the isolation (18-19 dB) between the two feed ports of two-antenna assemblies that are constructed and arranged in accordance with the present invention, without degrading the gain at the individual antenna ports. Further, the present invention does not increase the overall physical volume that is occupied by the multi-band antenna structure.
The design of a GSM/DCS/ISM Tri Band PIFA with two and three feed ports is described in above cited reference [4]. In this reference, multiple antennas are each of the PIFA type with all of the radiating elements lying on a single surface that is parallel to a ground plane. Prior art FIGS. 1-3, discussed below, show this type of arrangement.
In an embodiment of the present invention a multi-band, two-antenna assembly or module provides a combination of a PIFA and an inverted-F antenna (IFA) whose radiating elements are located in an orthogonal orientation.
An IFA is also known as a shunt-driven inverted-L antenna transmission line having an open end. That is, an IFA is a version of an inverted-L antenna having with the freedom to tap the input along the antenna""s horizontal wire in order to achieve a degree of control over the antenna""s input impedance.
FIG. 1 is a top view of a prior-art multi-band PIFA 10 having multiple feeds. FIG. 2 is a section view of PIFA 10 taken on line 2xe2x80x942 of FIG. 1, and FIG. 3 is a section view of PIFA 10 taken on line 3xe2x80x943 of FIG. 1. Multi-band PIFA 10 includes two separate feeds, one feed for each if its two frequency bands.
PIFA 10 includes radiating/receiving elements 11 and 12 that resonate at the two separate frequency-bands. Radiating/receiving elements 11 and 12 occupy a common plane, and they are positioned above and generally parallel to a ground plane element 13. An L-shaped slot 14 provides both physical and electrical separation between the two radiating/receiving elements 11 and 12.
A first hole 15 is provided in the relatively large area radiating/receiving element 11, and a conductive feed pin 16 is inserted through hole 15. Feed pin 16 is used to feed radio frequency (RF) power to radiating/receiving element 11. Feed pin 16 is electrically insulated from ground plane element 13 at the location whereat feed pin 16 passes through a hole that is provided in ground plane element 13.
A second hole 17 is provided in radiating/receiving element 11. A conductive post 18 which functions as a short circuit between radiating/receiving element 11 and ground plane element 13 is inserted through hole 17 and through a hole that is provided in ground plane element 13. Post 18 extends generally parallel to feed pin 16.
Radiating/receiving element 11, having the relatively larger dimensions of length (L1) and width (W1), resonates at the lower frequency band of multi-band PIFA 10.
Impedance matching of radiating/receiving element 11 is determined by the diameter of feed pin 16, by the diameter of shorting post 18, and by the distance that separates feed pin 16 and shorting post 18.
Radiating/receiving element 12, having the relatively smaller dimensions of length (L2) and width (W2), resonates at the higher frequency band of multi-band PIFA 10.
A first hole 19 is provided in radiating/receiving element 12. A conductive feed pin 20 is inserted through hole 19 and is used to feed RF power to radiating/receiving element 12. Feed pin 20 is electrically insulated from ground plane element 13 at the location whereat feed pin 20 passes through a hole that is provided in ground plane element 13.
A second hole 21 is provided in radiating/receiving element 12, and a conductive post 22 that passes through hole 21 provides a short circuit between radiating/receiving element 12 and ground plane element 13. Post 22 extends generally parallel to feed pin 20.
Impedance matching of radiating/receiving element 12 is determined by the diameter of feed pin 20, by the diameter of shorting post 22, and by the distance that separates feed pin 20 from shorting post 22.
Multi-band PIFA 10 illustrated in FIGS. 1-3 provides several disadvantages. For example, adequate isolation between the two frequency bands requires that a relatively large physical separation be provided between the two radiating/receiving elements 11 and 12, thus necessitating a relatively large width for L-shaped slot 14. This increased width of L-shaped slot 14 decreases the overall effective dimensions of PIFA 10, thereby reducing the bandwidth as well as the gain of PIFA 10.
In addition, any change that may be made in the frequency-separation that exists between the two resonant frequency bands of PIFA 10 involves a change in the linear dimensions L and W of the two radiating elements 11 and 12.
Z. D. Liu, P. S. Hall and D. Wake, xe2x80x9cDual Frequency Planar Invertedxe2x80x94F Antennaxe2x80x9d, IEEE Trans. Antennas and Propagation, Vol. AP-45, No. 10, pp. 1451-1548, Oct. 1997 describes a multi-band PIFA with separate feeds that is structurally configured similar to PIFA 10.
P. Kabacik and A. A. Kuchaski, xe2x80x9cOptimizing the Radiation Pattern of Dual Frequency Invertedxe2x80x94F Planar Antennasxe2x80x9d, JINA Conference, pp.655-658, 1998 (hereinafter referred to as:Kabacik et al) also describes a multi band PIFA having separate feeds that is similar to PIFA 10. However in Kabacik et al, instead of providing an L-shaped slot that separates the two radiating/receiving elements, as in PIFA 10, an annular slot is proposed by Kabacik et al.
The problem of mutual coupling within a dual-feed, multi-band, PIFA is a severe constraint or drawback for the utility of such an antenna in system applications. It is possible to improve the isolation between the multiple radiating/receiving elements of a multi-band PIFA by increasing the separation distance between the radiating/receiving elements. In view of an emphasis on reducing the physical size of internal cellular antennas, this recourse of providing an increased physical separation between the radiating/receiving elements is not a practical solution.
The present invention provides a two-antenna assembly, one antenna of which is a PIFA. The second antenna of the two-assembly is contained within a physical volume that is occupied by the PIFA, such that the overall physical volume that is occupied by a two-antenna assembly in accordance with the invention is equal to the physical volume of the PIFA.
In embodiments of the invention, the second antenna""s radiating/receiving element is mounted between the radiating/receiving element of the PIFA and a ground plane element, and the second antenna""s radiating/receiving element extends in a plane that is perpendicular to both the plane of the radiating/receiving element of the PIFA and the plane of the ground plane element.
In other embodiments of the invention, the second antenna""s radiating/receiving element is mounted between the radiating/receiving element of the PIFA and a ground plane element, and the second antenna""s radiating/receiving element extends in a plane that is parallel to both the plane of the radiating/receiving element of the PIFA and the plane of the ground plane element.
The present invention provides a combined PIFA/IFA two-antenna assembly whose construction and arrangement retains the physical volume of the PIFA, and in addition minimizes the mutual coupling between the radiating/receiving elements of the two-antenna PIFA/IFA assembly.
In accordance with the invention, the PIFA portion of the two-antenna assembly is designed for dual resonance (i.e. AMPS/PCS resonance or GSM/DCS resonance) in the cellular frequency bands.
The PIFA is constructed and arranged such that the plane of the PIFA""s radiating/receiving element is parallel to a flat or planar ground plane element, thereby providing a physical space between the PIFA""s radiating/receiving element and its ground plane element.
In accordance with the invention, the second antenna portion (the IFA portion) of the two-antenna assembly operates in a frequency band for a non-cellular application (i.e. ISM or GPS), and the second antenna portion is constructed and arranged such that its radiating/receiving element is located in the space that exists between the radiating/receiving, element and the ground plane element of the PIFA.
In an embodiment of the invention the plane of the second antenna""s radiating/receiving element extends generally parallel to the plane of the PIFA""s radiating/receiving element.
In other embodiments of the invention the plane of the second antenna""s radiating/receiving element extends generally perpendicular to the plane of the PIFA""s radiating/receiving element.
In order to provide a Tri band two-antenna assembly within the volume that is occupied by the PIFA, in one embodiment of the invention the perpendicular-oriented radiating/receiving element of the IFA is placed (generally underneath a radiating or non-shorted edge of the PIFA""s planar radiating/receiving element. This results in a orthogonal disposition of the planar radiating/receiving element of the PIFA and the planar radiating/receiving element of the IFA.
Apart from the orthogonal orientation of the two planar radiating/receiving elements, a slot contour within the radiating/receiving element of the PIFA also improves the isolation between the two feed ports that are individually provided for the PIFA and the IFA.
In other embodiments of the invention the above-described perpendicular-oriented radiating/receiving element of the IFA is placed under a non radiating or shorted edge of the PIFA""s radiating/receiving element. This arrangement also results in an orthogonal disposition of the planar radiating/receiving elements of the PIFA and the IFA, this orthogonal orientation also providing isolation between the feed port of the PIFA and the feed port of the IFA.
In addition, neither of the above constructions and arrangements require that an increased physical separation be provided between the radiating/receiving elements of the PIFA.
This invention provides a dual-feed Tri-band (AMPS/PCS/ISM band or GSM/DCS/ISM band) two-antenna assembly having good gain, having a reasonable bandwidth and having improved isolation, such as xe2x88x9218 dB, between the multiple feed ports of the two-antenna assembly.
This invention provides a dual-feed Tri-band (AMPS/PCS/GPS bands) two-antenna assembly having good gain, having a reasonable bandwidth and having improved isolation better than xe2x88x9218 dB between the multiple feed ports of the two-antenna assembly.
In accordance with the invention the physical volume that is required by the IFA is physically placed within the volume that is required by the PIFA. In such an arrangement, the radiating/receiving element of the IFA is located under the radiating/receiving element of the PIFA, and the radiating/receiving element of the IFA may be either parallel-to or perpendicular-to the radiating/receiving element of the PIFA.
Although the advantage of improved isolation is reduced when the radiating/receiving element of the IFA is under and parallel-to the radiating/receiving element of the PIFA, this construction and arrangement in accordance with the invention improves the gain within the ISM band of the IFA, and in addition the bandwidth of both the PIFA and the IFA is improved.
This invention provides a bandwidth characteristic and an isolation characteristic for several planar, compact, dual-feed, Tri band/Quad band. two-antenna assemblies having utility in both cellular and non-cellular applications.
Within the spirit and scope of this invention, the invention can also be utilized to improve the isolation performance of a dual-feed, dual-band, PIFA two-antenna assembly wherein the PIFA provides for either AMPS or GSM operation, and wherein the IFA provides for PCS or DCS or ISM or GPS operation.
An important feature of the invention is minimizing the coupling between the two-antenna assembly""s multiple radiating/receiving elements, which in turn improves the isolation between the individual feed ports that are provided for each of the radiating/receiving elements.
The present invention provides a two-antenna assembly that is formed by a new and an unusual combination of a PIFA and an IFA. The construction and arrangement of the two-antenna assembly results in minimizing the mutual coupling between the two antenna feed ports, without increase in the physical volume that is required by the PIFA itself. The present invention""s technique for improving the isolation between the two antenna feed ports also retains the desirable physical compactness requirement of a multi-band two-antenna assembly.
The present invention""s improvement in isolation between the two antenna feed ports that individually support the cellular band and the noncellular band does not result in a deterioration of the radiation/polarization characteristics of the radiating/receiving elements.